This investigation is designed to improve the diagnosis and management of venous thromboembolic disease. Initial data from this project suggest that Doppler ultrasound is more accurate than strain gauge plethysmography in detection of phlebographically proven deep vein thrombosis, including calf vein thrombosis. Preliminary results suggest that lung scanning (both perfusion and ventilation) is both insensitive and nonspecific in identifying or excluding pulmonary emboli as validated by pulmonary arteriography. Initial experience suggests that screening leg veins for a source of emboli is more predictive of the presence or absence of pulmonary embolism. The final year of this proposal will test the hypothesis that noninvasive screening for deep vein thrombosis will significantly improve the diagnostic accuracy of lung scanning in evaluating patients for suspected pulmonary embolism. All consenting patients will undergo preliminary Doppler ultrasonic venous examination followed by radionuclide phlebography and ventilation-perfusion lung scans. Comfirmatory pulmonary arteriography will then be carried out. The results will be analyzed independently for sensitivity, spcificity and predictive value in detection or exclusion of pulmonary emboli.